1. Field of the Disclosure
This disclosure relates generally to apparatus and methods for a wireless LAN client. More particularly, the disclosure relates to an apparatus and method for listen interval (LI) selection for a wireless local area network (WLAN) client.
2. Related Art
With the increased popularity of social networking in today's world, the need for smart phones to connect to a network has become very prominent. WLAN technology (following the IEEE 802.11 protocol) is one of the key and cost efficient technologies, which allows smart phones to connect to a network. Because smart phones are battery powered devices, the challenge for WLAN is to maintain connectivity with a backbone network with reduced power consumption, especially during standby (no traffic condition). WLAN power consumption accounts for a significant portion of overall battery power, thereby affecting the standby time of a smart phone. It is desirable to reduce the standby power of a smart phone, thereby significantly increasing the standby time of the smart phone. The following briefly describes the power save protocol as provided by the IEEE 802.11 specification.
According to the IEEE 802.11 specification, a wireless station (STA), such as a smart phone, specifies a listen interval (LI) during an association phase (e.g., set up) with a wireless access point (AP). The LI determines how frequently the STA wakes up to listen to a beacon signal that is periodically transmitted from the AP. For example, a LI of 2 may be selected to cause the STA to wake up to receive every other beacon signal transmitted from the AP. In addition, the STA should also follow the DTIM beacon (Delivery Traffic Indication Message) output by the AP for the broadcast frames to be delivered after the DTIM beacon. If the STA ignores broadcast frames, it can follow the LI specified during the association phase. If the LI is specified as a high value, power consumption may be significantly reduced. However, the high LI value will adversely affect the performance of the WLAN link, because the STA will have to sense traffic that has been buffered at the AP for a long time. For example, if the beacon interval is 100 ms and the LI specified by the STA is 5, a worse case latency of 500 ms (5×100 ms) is introduced for sensing the presence of buffered frames on the AP. This latency continues to be present for fetching the downlink frames whenever the STA enters a power save mode. For these reasons, it is common for the LI to be set to 1, such that the STA wakes up to listen for each beacon signal, thereby reducing latency on the data path. However, this raises a concern with respect to increased power consumption by the STA.